Need some diagnostic direction

[Sonofbumperbolt]

I am working on a recently acquired 1993 Explorer XLT 4x4. It has 78,000 miles. I am dealing with a high idle/poor fuel economy issue. It is throwing 136/172 codes (lean, both banks). KOEO gives 111. The MAF sensor checks out good. The IAC valve is new. Live data shows the O2 sensors switching values from 0.17 to 0.80. The IAT sensor reads around 2.5v. The ECT sensor reads normal for a warm engine. All sensor and electrical seems to indicate integrity on the ECM side of things. I have used carb cleaner and propane to check UIM gasket leaks. None are readily apparent.
A fuel pressure gauge reveals 32 psi at idle with vacuum and 40 psi at idle with no vacuum. When shutting off a warm engine the fuel pressure bleeds off to 3 psi in one minute and 0 psi in two minutes. A cold engine key on gives around 35 psi then drops quickly to zero.
I have been over the vacuum lines several times and haven't found any leaks. I used a screwdriver to the ear to check injectors and all are clicking.
Anyone have any ideas? Is the fuel rail bleeding off too quickly? Possibly an injector stuck? Any help is appreciated.

 

[FR-425]

Yep,

Throttle body spacer is in up-side-down

 

[Carguy3J]

Yep,

Throttle body spacer is in up-side-down

???? What are talking about? There is no throttle body "spacer" on these engines/vehicles. The later SOHC has a thick gasket, that is sort-of a spacer, but is impossible to put it in upside down.

I am working on a recently acquired 1993 Explorer XLT 4x4. It has 78,000 miles. I am dealing with a high idle/poor fuel economy issue. It is throwing 136/172 codes (lean, both banks). KOEO gives 111. The MAF sensor checks out good. The IAC valve is new. Live data shows the O2 sensors switching values from 0.17 to 0.80. The IAT sensor reads around 2.5v. The ECT sensor reads normal for a warm engine. All sensor and electrical seems to indicate integrity on the ECM side of things. I have used carb cleaner and propane to check UIM gasket leaks. None are readily apparent.
A fuel pressure gauge reveals 32 psi at idle with vacuum and 40 psi at idle with no vacuum. When shutting off a warm engine the fuel pressure bleeds off to 3 psi in one minute and 0 psi in two minutes. A cold engine key on gives around 35 psi then drops quickly to zero.
I have been over the vacuum lines several times and haven't found any leaks. I used a screwdriver to the ear to check injectors and all are clicking.
Anyone have any ideas? Is the fuel rail bleeding off too quickly? Possibly an injector stuck? Any help is appreciated.

That leakdown rate, on the fuel pressure, is WAY too fast. You have a problem in your fuel system somewhere. Either a leaky injector, an actual leak in a line somewhere (but you would probably smell that), or a problem with the pump. I'm not sure of the exact spec, but the system should hold pressure much longer then that.

 

[Sonofbumperbolt]

The leak down rate was my concern also. I tested my 97 Escort with the same gauge. It gave almost identical numbers but held pressure for a much longer time than the Explorer. I'm not seeing or smelling any gas leaks on the vehicle.

 

[Carguy3J]

The leak down rate was my concern also. I tested my 97 Escort with the same gauge. It gave almost identical numbers but held pressure for a much longer time than the Explorer. I'm not seeing or smelling any gas leaks on the vehicle.

A.) Leaky injector(s) bleeding fuel into the cylinders after shutdown. Pull plugs and sniff. Check oil and sniff.

B.) Bad pressure regulator, bleeding pressure back in to the tank. Test methods are easily found here, google, or Chilton/Haynes manuals.

C.) In-tank pump is leaking internally and unable to hold the pressure when not running. Not sure how to test that. Have fun pulling the tank in the cold.

 

[FR-425]

Oops wrong year, my bad, disregard.

Perfect, did I mention I'm perfect.!

 

[Sonofbumperbolt]

A.) Leaky injector(s) bleeding fuel into the cylinders after shutdown. Pull plugs and sniff. Check oil and sniff.

B.) Bad pressure regulator, bleeding pressure back in to the tank. Test methods are easily found here, google, or Chilton/Haynes manuals.

C.) In-tank pump is leaking internally and unable to hold the pressure when not running. Not sure how to test that. Have fun pulling the tank in the cold.

A) Will check.
B) FPR vacuum line checked. It is dry.
C) If you think I'm pulling the tank you're wrong. Access panel FTW!

 

[Sonofbumperbolt]

This afternoon I plugged the return line and pressurized the system. It did not hold pressure. If I'm thinking right then that points to an injector, correct? I pulled the plugs to see if any were fouled that might point to a bad injector. Five of the plugs were Bosch (eww) platinums and one was a MC platinum. The #5 plug was fouled fairly bad with the #2 plug being not as bad. The rest of the plugs were very clean and looked healthy.

 

[Sonofbumperbolt]

So if I decide to replace a bad injector is there a way to pinpoint the bad injector or do I do all six and call it good?

 

[Sonofbumperbolt]

Also I am getting some oil dilution but no wet plugs.

 

[Sonofbumperbolt]

I removed the upper intake manifold to inspect the injectors. What do I find but the gasket between the fuel rail and the lower intake manifold had failed clear in the back. I am going to repair that and address the fuel pressure next.

 

[Sonofbumperbolt]

 

[zman1995]

Throttle position sensor......I dont remember if these had it, but that is what it would be in a f150 with those symptoms

 

[Sonofbumperbolt]

So to sum it all up this is what was wrong with our Explorer:
1) The retaining tabs on the air box were broken allowing dirt and contaminants into the intake. I picked up a good one from the local salvage yard.
2) The MAF was dirty to the point I replaced it with a new unit.
3) The purge valve solenoid tee was broken and leaking vacuum. Replaced with new.
4) The thermostat was stuck open so I replaced it with new.
5) The ECT was throwing an out of range code so I installed a new one when I did the thermostat.
6) The UIM gasket under the fuel rail had failed, causing more vacuum leakage. Replaced same.
7) The IAC valve was not functioning right so I replaced it also.
After all of this our Explorer idles and runs exceptionally well. The 4 of us traveled in it for 8.5 hours round trip for Christmas and averaged just over 18 mpg, all the while riding in comfort.

 

[Sonofbumperbolt]

My daughter has been driving this explorer to school every day for the last couple of months. I have noticed it was using about a quart of oil every 1300 miles. I tightened the lower intake manifold bolts and seemed to have fixed the problem. My daughter and I drove to Denver last weekend and put just over 1100 miles on it. The oil didn't move on the dipstick and we averaged 19.5 mpg round trip.

 

[FR-425]

Nice! Just the scheduled 21 year tune up then.

 

[teletekman]

Nice looking Ex btw!

 

[Sonofbumperbolt]

Thanks for the comments gentlemen. I am really happy with this rig overall. I am considering a gear change from the 3.27 to 3.55 ratio as it doesn't handle some hills around here.

 

[FR-425]

Go with the 3.73 Limited slip.

May as well source the entire axle out of a later model and upgrade to rear disk brakes as well. Bolt in swap. Major braking improvement.

Much simpler and cheaper than re-gearing.

 

[teletekman]

Go with the 3.73 Limited slip.

x2.

I kiss my rear it's such a great rear on my rig.